Oil burner with widely variable operating range



Nov. 15, 1966 T. s. VOORHElS OIL BURNER WITH WIDELY VARIABLE OPERATINGRANGE Filed April 15, 1965 INVENTOR. TEMPLE 8. VOORHEIS WWW ATTORNEYSUnited States Patent 3,285,315 OIL BURNER WITH WIDELY VARIABLE OPERATINGRANGE Temple S. Voorheis, Palo Alto, Calif., assignor to Coen Company,Burlingame, Califl, a corporation of California Filed Apr. 15, 1965,Ser. No. 448,303 7 Claims. (Cl. 158-28) This invention relates to aburner for combustion chambers of the type used for firing commercialand marine apparatus, such as, for example, water tube boilers and thelike. More particularly, the invention relates to such burner that hasan extremely wide load range.

For convenience of description the objects of the present invention willbe stated in terms of a burner for firing a marine boiler of the typeused for producing steam that is supplied to the turbine that providesmotive power for a water-borne vessel. A boiler operating in suchenvironment must be capable of providing steam over widely varyingoperating ranges. For example, far more steam is needed when a vessel isunder way than when it is standing by. In the latter condition, althoughvirtually no steam is required, it is impractical to interrupt theburner operation since start-up is a timeconsuming and dangerousoperation. In the prior art steam-producing systems, one or moreenginemen were stationed at a plurality of boilers so that one or moreboilers could be manually turned down at lower ranges of steam demand.Such mode of operation, in addition to being expensive from thestandpoint of required manpower, is slow in that each time that a boileris turned down and restarted it must be purged of residual fuel andproduces much soot and smoke during the light-off procedure. Moreover,it has been found that the majority of explosions and other accidentsoccur during light-off.

The principal object of the present invention is the provision of aburner having such a wide range of operation that the burner can beturned down to approximately of its full rated capacity. Such object isachieved by providing two or more fuel lines extending through a throatinto a combustion chamber and by providing on each such fuel line aburner cap in which are formed fuel passageways so oriented that eachfuel line supplies fuel to a discrete sector of the combustion chamberinterior. Means are provided for totally arresting or shutting off thefuel supply through one or more of the fuel lines so that at lowerranges, less than all of the fuel lines are supplying fuel to thecombustion chamber. At

such low range of operation the heat output of the burners is minimalbut is sufficient to sustain combustion and ready the burner for turn-upwith the advent of increased demand.

Another object is to provide an improved burner cap having fuel passagesformed therein in such pattern and orientation that the combustionchamber is provided with a uniform flame pattern at full andintermediate ranges of operation. In the specific example, described inmore detail hereinafter, two burner caps are shown and each has pluralfuel passages arranged in a generally semicircular pattern so that thetwo caps in combination will afford uniform and complete distribution offlame within the combustion chamber. In such specific example, a fantailflame is desired, one that is extensive in one direction and thin in adirection transverse of the first-mentioned direction. Burner caps fordeveloping such flame pattern are provided with individual fuel passagesformed at different angles with respect to the central axis of theburner throat to accomplish the necessary flame distribution.

A further object is to provide a cap of the type referred to above inwhich the amount of fuel emanating from each fuel passageway is uniform.In understanding this object it should be appreciated that atomizers formixing with fuel oil such gaseous materials as steam, air or combustiblegas are employed wherein the oil and/or gaseous material is spun orwhirled to enhance the atomization and emulsion thereof. Such atomizingstructure is located upstream of the burner cap as a consequence ofwhich the atomized fuel arriving at the burner cap is whirling orspinning with respect to the longitudinal axis of the fuel line. It hasbeen found empirically in respect to caps lacking fuel passagewaysthroughout the entire periphery of the cap that fuel flow through eachof the various passages will be different due to the whirling orspinning of the atomized fuel. The present invention includes on theinterior of the cap a hemispherical surface on which a dam is formedopposite that portion of the cap in which the fuel passages are formed.Although the theoretical justification for such dam is not fullyunderstood at this time, it is believed that the darn interrupts ordeflects the whirling motion of the atomized fuels such that eachpassageway is provided with a uniform amount of fuel.

Other objects, features and advantages of the present invention will bemore apparent after referring to the following specification andaccompanying drawing in which:

FIG. 1 is a partially schematic view of a burner of the presentinvention installed in a burner throat through a wall of the combustionchamber;

FIG. 2 is an elevation view of the burner taken, at an enlarged scale,substantially along line 2-2 of FIG. 1;

FIG. 3 is an elevation view of a burner cap constructed in accordancewith the present invention; and

FIG. 4 is a cross-sectional view taken along line 44 of FIG. 3.

Referring more particularly to the drawing, reference numeral 12indicates the wall of a combustion chamber of a furnace, for example, aboiler furnace, which wall includes refractory lining 14 and a burnerthroat 16 extending from the interior of the combustion chamber to theexterior of wall 12. In FIG. 1 the interior of the combustion chamber isat the top of the picture. Mounted exteriorly of the combustion chamberon the outer surface of wall 12 is a Windbox 18 for directing anddistributing air into throat 16 from a duct 20 that is supplied with airby a conventional blower or fan not shown. Windbox 18 can be providedwith known air control and distributing devices such as the typedisclosed in detail in my US. Patents 2,838,103 and 2,889,871. Such airflow control systems aiford a uniform air flow through throat 16 withoutimparting unnecessary spiral or radial components of force to the air asit emanates into the combustion chamber interior.

Extending through Windbox 18 and into throat 16 are first and secondfuel lines 22 and 24. Such fuel lines typically include concentricpassages for fuel 25F and for an atomizing medium 25S such as steamwhich are mixed at an atomizer, designated schematically at 26, prior todelivery to the inner ends of the fuel lines. Fuel supplied throughlines 22 and 24 is controlled by a throttle valve 28 which is suppliedfrom a conventional source of fuel oil (not shown) through a fueldelivery line 30. Valve 28 is controlled by a conventional controllersystem 32 in accordance with the demands of the combustion chamber orfurnace being fired by the burner which controller also has provisionsfor controlling the quantity of air delivered through duct 20. Sincecontroller 32 is not part of the present invention and since manycontrollers for accomplishing the desired mode of operation 3 are knownin the art, further detailed description of the controller will not behere necessary.

One of fuel lines 22 and 24, for example, fuel line 22, is provided witha solenoid valve 34 which is operative to totally arrest flow throughline 22 when the valve is actuated.

The operation and control of valves 28 and 34 by controller 32 can beunderstood by first assuming that the burner is firing at a range ofbetween full capacity and about of full capacity. In such range,controller 32 adjusts valve 28 and the amount of air supplied throughduct to maintain the proper fuel-air mixture necessary to supply theload within the combustion chamber. At a point typically around 10% offull operating capacity, controller '32 acts to close solenoid valve 34so that the amount of fuel supplied to the combustion chamber is halvedwhereas the amount of air supplied to the combustion chamber remainsconstant. It may be seen therefore that the burner is operating at about5% rated capacity when solenoid valve 34 is actuated to arrest the fuelflow through line 22. Such level of operation has been found in marineboilers, for example, to be adequate to maintain proper temperatureswithin the combustion chamber and to generate sufiicient steam to powerauxiliary equipment. Such point of operation of the system howeverprovides no steam for operation of the main motivating turbine. Ofcourse, when steam demand increases, controller 32 acts to open solenoidvalve 34 and throttle valve 28 thereby increasing heat output of theburner. Since the interior of the combustion chamber is not reduced to adangerously low temperature level even when valve 34 is closed, thetemperatures necessary for the increased load are rapidly reachedwithout any danger that liquid fuel will be admitted into the combustionchamber before it is totally atomized and ignited.

Each fuel line 22, 24 has on the inner end thereof a cap 36 and 38,respectively, that resides in a shield 40 within burner throat 16 (seeFIG. 2). In the example here under consideration there are two fuellines and consequently two caps disposed in an oval or elliptic throat.Such showing is only exemplary, however, because throats of otherconfigurations with other numbers of caps are deemed equivalent.

The internal details of the preferred form of the caps 36 and 38 can beseen in FIGS. 3 and 4. Since both caps are identical, only cap 38 willbe described in detail. The cap includes an interiorly-threaded flange42 for securing the cap to the inner end of fuel line 24. The cap has anend wall 44 formed on the interior thereof with a generaly hemisphericsurface 46 of a diameter approximately equal to the inner diameter offuel line 24. The outer surface of end wall 44 defines a frusto-conioalsurface portion 48. Parallel shoulders 50 and 52 are provided on the endcap for defining a wrench grip useful in installing and orienting thecap. Fuel passages are provided in, end wall 44 and extend fromhemispheric surface 46 to frustoconical surface 48. The fuel passagesare oriented so as to distribute the fuel within the combustion chamberin a desired manner. For this purpose, and as can be seen more clearlyin FIG. 3, the holes are limited to a 180 or semi-circular portion ofthe cap. Such showing is merely exemplary of the required relationshipthat fuel openings are limited to a sector of the cap that extends (indegrees) around the cap by an amount approximately equal to a fractionhaving a numerator of 360 and a denominator N equal to the number offuel caps provided in burner throat. In the exemplary cap here shownthere are two caps as a consequence of which all fuel openings arerestricted to an approximate 180 portion of end wall 44.

At the center of the 180 portion is formed a passageway 54 that isparallel to a line extending between the centers of caps 36 and 38 whichline in the present example is horizontal. The passageway 54 is,however, slanted outwardly at a rather steep angle with respect to thelongitudinal axis of fuel line 24 so that fuel is supplied to thelateral or side portions of the combustion chamber. Above and belowpassageway 54 are second passageways 56, each of which is formed at alesser angle with respect to the central longitudinal axis of fuel line24 but slanted slightly away from horizontal. Accordingly, fuel issuingthrough passageway 56 is spread laterally to a lesser extent butupwardly and downwardly to a greater extent than is the case with fuelissuing from passageway 54. Spaced from passageways 56 are thirdpassageways 58 that are formed at still a smaller lateral angle withrespect to the central axis of fuel line 24. The passageways 58 have buta slight component in the lateral direction but distribute the fuelupwardly (or downwardly) within the combustion chamber. It can be seenthat the above-described orientation of passageways 54, 56 and 58effects a uniform distribution of fuel within one-half of the combustionchamber and that installation of fuel cap 36 with identical passagewaysoppositely disposed will effect uniform fuel distribution within theother half of the combustion chamber.

Allusion has been made hereinabove to atomizer 26, a conventionalexpedient for intimately intermixing a gaseous medium with the fuel oilso as to promote mixture with combustion air and combustion. Suchatomizers typically include a whirl plate 59 or the like that impartsswirl as at arrow 598 to the atomizing medium and the fuel oil topromote the mixture. Fuel arriving in the chamber defined by hemisphericsurface 46 within cap 38 is therefore swirling rapidly with respect tothe central axis of fuel line 24. In order to obtain uniform fueldelivery to each passageway 54, 56, 58, there is provided a dam -60affixed to hemispheric surface 46 and located in the portion of cap 38opposite the'portion in which the fuel passageways are defined. Dam 60includes a longitudinally-extending wall 62 and a laterally-extendingwall 64. Each wall is formed by a fiat plate having an arcuate surfacethereon that has a radius of curvature equal to that of hemispheric wall46. Consequently, the dam can be elfectively secured to the hemisphericwall. As can be seen most clearly in FIG. 3, longitudinally-extendingwall 62 is spaced laterally of the central axis and on the side thereofopposite from the fuel passageways. The dam has been found effective indistributing the fuel uni- -formly over the five passageways so as toafford uniform flame distribution within the combustion chamber.

Referring again to FIG. 1, it will be seen that when fuel is suppliedthrough both fuel lines 22 and 24, a generally fantail-shaped flame isdeveloped and the entire boiler furnace interior is supplied with flame.As the operating rate is reduced to a point at or about 10% of capacity,solenoid valve 34 is closed, thereby arresting fuel flow through fuelline 22 and its associated cap 36. It has been found in one installationof a burner of the present invention that a flame pattern of the generalform depicted at 66 in FIG. 1 is formed. That is to say, one-half of theboiler is being fired at a reduced rate; the other half is not beingfired at all. The uniform movement of air through the throat ismore thansuflicient to support combustion of the atomized oil emanating from thecap 38 and to promote heat distribution within the boiler so as to avoiddangerous temperature differentials across the water tubes andcombustion chamber walls. However, sufficient heat to light-off fueloilfrom cap 36 when valve 34 is again opened is maintained in thecombustion chamber so that operation from only one fuel line (24) issufficient to provide safe minimum load operation and to avoid damage tothe boiler interior.

. Thus it will be seen that the present invention provides a burnersystem capable of an extremely wide operating range; in one installationsafe operation at 5% of rated capacity was accomplished. The inventionadditionally provides a burner that is readily adapted to automatedoperation in that no boiler needbe continuously shut down and re-litas'the load demands vary. '7

Although one embodiment of the invention has been shown and described,it will be obvious that other adaptations and modifications can be madeWithout departing from the true spirit and scope of the invention.

I claim:

1. In combination with a combustion chamber having a wall defining aburner throat therein and means for providing combustion air to saidchamber through said throat, an improved fuel oil supply systemcomprising a plurality of fuel lines extending through said throat intosaid combustion chamber, each said fuel line having on the inner endthereof a cap, each said cap having at least one obliquely oriented fuelpassage therein for diver-gently directing fuel into a discrete sectorof said combustion chamber, the totality of said caps and said fuelpassageways being oriented so that all sectors of the combustion chamberare supplied with fuel when fuel is supplied from all said caps, meansfor controlling the amount of combustion air and fuel supplied to saidcombustion chamber over a range in accordance with the load demand ofsaid combustion chamber, and means operable at the low end of the rangeof fuel flow to arrest fuel flow through at least one of said fuel linesand less than all said fuel lines so that less than all sectors of saidcombustion chamber are fired at the low end of the range.

2. A variable load burner for a combustion chamber comprising a wallforming a boundary of the combustion chamber and having a burner throattherein, first and second fuel lines extending into the combustionchamber through said throat, first and second nozzle caps mounted on theinner end of respective said fuel lines, each said nozzle cap defining agenerally semicircular pattern of fuel openings therein, said nozzlecaps being oriented so that fuel openings in one said cap arefurthermost from openings in the other said cap, thereby affording afantail flame symmetrical relative the central axis of the throat, meansfor throttling the fuel supplied to said fuel lines, and means operableat a low rate of fuel supply for arresting fuel flow to one said nozzle.

3. A burner for a combustion chamber comprising first and second fuellines for supplying fuel to said combustion chamber, means in each saidline for atomizing and swirling fuel therein, a cap mounted on the innerend of each said fuel line, each said cap having a generally hemisphericsurface interiorly thereof and a generally frusto-conical surfaceexten'orly thereof, a plurality of fuel passages extending from saidinterior surface to said exterior surface, said holes being disposed inone-half of said cap, a dam formed interiorly of said cap on theopposite half from said holes, said dam having a first planar facenormal to the axis of its associated fuel line and a second planar faceperpendicular to said first face and lying in a plane parallelly spacedfrom the central axis of said line, and means for totally arresting fuelflow to one said fuel line at a low operating point thereof.

4. An oil fired burner for controllably injecting fuel and air into acombustion chamber of the type having a wall forming one boundary of thecombustion chamber, said burner comprising a portion of said wall havinga refractory throat opening therethrough, said throat having an ovalcross-sectional shape that has its greatest dimension along a majordiametral axis, first and second fuel lines mounted in said throat inspaced relation along said major axis, a cap mounted on the inner end ofeach said fuel line, each said cap including a plurality of orificesformed in a generally semicircular pattern therein, the orifices remotefrom said diametral axis being formed at a first angle with respect tothe central axis of the orifice, the orifices proximate said diametralaxis being oriented at a second angle with respect to the central axisof the orifice, said second angle being greater than the first angle sothat a generally fan shape flame pattern that is flattened along theplane of said diametral axis is produced, means for supplying fuel tosaid fuel lines, and means for supplying air through said throat tosupport combustion of said fuel in said combustion chamber. 1

5. A burner according to claim 4 including controller means forcontrollably throttling fuel and air delivered to said burner inaccordance with the load demand thereon, valve means in said first fuelline for totally arresting fuel flow therethrough; and means operativelyconnecting said valve means to said controller means for arresting fuelflow through said first fuel line at a preselected low point ofoperation of said burner, whereby upon arresting fuel flow through saidfirst fuel line, said burner fires only through said second fuel lineand its associated cap.

'6. A burner according to claim 4 including means in said fuel lines foratomizing fuel oil therein by intermixing a gaseous medium therewith byswirling, whereby fuel arriving at said caps is moving in a spiral path,and means in said cap for defining a dam, said dam being disposedoppositely of said orifices and having a first wall aligned parallel tothe central axis of said fuel and a second wall normal to said firstwall and extending therefrom in a direction opposite from said orificesso that spirally moving fuel impinging on said dam is distributeduniformly to said orifices. v

7. The improved oil supply system of claim 1 comprising N fuel linesextending through said throat in substantially symmetrically spacedrelation relative the central axis of said throat, the fuel passage ineach cap being limited to a sector thereof further-most from the centralthroat axis, said sector having radial extent limited to 360/N degrees,wherein N is a positive integer.

References Cited by the Examiner UNITED STATES PATENTS 1,229,030 6/1917Cecil.

1,536,230 5/1925 McCue 158-28 2,315,412 3/1943 Galumbeck 158-28 X3,180,395 4/1965 Reed 15876 X JAMES W. WESTI-IAVER, Primary Examiner.

1. IN COMBINATION WITH A COMBUSTION CHAMBER HAVING A WALL DEFINING ABURNER THROAT THEREIN AND MEANS FOR PROVIDING COMBUSTION AIR TO SAIDCHAMBER THROUGH SAID THROAT, AN IMPROVED FUEL OIL SUPPLY SYSTEMCOMPRISING A PLURALITY OF FUEL LINES EXTENDING THROUGH SAID THROAT INTOSAID COMBUSTION CHAMBER, EACH SAID FUEL LINE HAVING ON THE INNER ENDTHEREOF A CAP, EACH SAID CAP HAVING AT LEAST ONE OBLIQUELY ORIENTED FUELPASSAGE THEREIN FOR DIVERGENTLY DIRECTING FUEL INTO A DISCRETE SECTORAND OF SAID COMBUSTION CHAMBER, THE TOTALITY OF SAID CAPS AND SAID FUELPASSAGEWAYS BEING ORIENTED SO THAT ALL SECTORS OF THE COMBUSTION CHAMBERARE SUPPLIED WITH FUEL WHEN FUEL IS SUPPLIED FROM